Anyone have any suggestions for a DIY headphone amp? I was looking into the SSMH, but I'd rather use something with a 12VDC power supply instead of a 48VDC one. I toyed around, and designed this:
I substituted 6J6's for the 19J6's called for in the original SSMH design, and replaced the 48VDC PSU with a 12VDC PSU. From there, I adjusted the resistors accordingly to keep the gate-source voltage at 5v. I am fairly new to DIY headphone amps, so I wanted a "pro" to take a look at it first. So, be nice?
The picture has a few typos; you need a ~1-2A @ 12VDC PSU, not a .5A one, and the "48V" should obliviously read "12V".
An externally hosted image should be here but it was not working when we last tested it.
I substituted 6J6's for the 19J6's called for in the original SSMH design, and replaced the 48VDC PSU with a 12VDC PSU. From there, I adjusted the resistors accordingly to keep the gate-source voltage at 5v. I am fairly new to DIY headphone amps, so I wanted a "pro" to take a look at it first. So, be nice?
The picture has a few typos; you need a ~1-2A @ 12VDC PSU, not a .5A one, and the "48V" should obliviously read "12V".
Gwah, I thought the "6" in "6J6" meant 6v. Anywho, not to be a bother, but would you have a suggestion on what to change out? Pardon my noobiness; I am willing, and wanting, to learn.
Note that you will need to add resistance in series with the filaments as they form part of the output circuit, and you want to drop ~ half of the supply voltage across the FET and the other half across the resistor-filament combination for best linearity, and at a certain point excess voltage across the FET means excessive dissipation.. Go back the original circuit and calculate the series resistance based the filament current and as designed source voltage.. I think 51 ohms might be close enough **but check it** 5W resistor min...
Also Pete is a regular here, you might just send him a PM and see what changes he suggests to use the 6J6...
Also Pete is a regular here, you might just send him a PM and see what changes he suggests to use the 6J6...
So like this? I was wondering exactly what goes where; I can't visualize it without a diagram.
Referring to the modified schematic you posted in the first post of this thread you would add the resistors in series with the filaments of the 6J6.. I didn't see any schematics on the other site you referenced.
Also I really would contact Pete and ask him for his thoughts on this.. There are several threads here on related designs.
I was notified by a very helpful person about this thread. In my case, it may be a bit of the blind squirrel found the right nut. It was in the vein of Nelson's "just build it and try it". This will be brief for now - I'm at work.
I built a CRC supply with a hefty enough toroid that under load was about 49 to 50 V. I used IRF610 mosfets. So what I did was build everything else to Pete's specs.
At the source pin of the mosfet, I attached two car panel indicator bulbs in parallel. The bulbs were rated at about 12 to 14V and at 250mA. The bulbs were then attached to one of the heater pins and the other heater pin to ground.
I then hooked it all up to a variac and measured the volts on the heater to make sure I wasn't cooking the tubes at above recommended heater voltages.
Here's where the blind squirrel part comes in. Somehow, IIRC, at full wall voltage, the heaters came in right about 6.1V or so. So the MOSFET was happy, the bulbs were happy, and the tube heater was happy. The 1 BIG caveat is that running a MOSFET at 450 mA dissipates mucho mucho heat. I needed to get a good chunk of aluminum for each MOSFET. I've not worked on it for about 5 months. I've decided to power the heaters with V regs so that I can run the mosfets at a lower current. It was hot but sounded nice. I got several compliments on the sound at LSAF this year although it looked like Frankenstein's monster.
I built a CRC supply with a hefty enough toroid that under load was about 49 to 50 V. I used IRF610 mosfets. So what I did was build everything else to Pete's specs.
At the source pin of the mosfet, I attached two car panel indicator bulbs in parallel. The bulbs were rated at about 12 to 14V and at 250mA. The bulbs were then attached to one of the heater pins and the other heater pin to ground.
I then hooked it all up to a variac and measured the volts on the heater to make sure I wasn't cooking the tubes at above recommended heater voltages.
Here's where the blind squirrel part comes in. Somehow, IIRC, at full wall voltage, the heaters came in right about 6.1V or so. So the MOSFET was happy, the bulbs were happy, and the tube heater was happy. The 1 BIG caveat is that running a MOSFET at 450 mA dissipates mucho mucho heat. I needed to get a good chunk of aluminum for each MOSFET. I've not worked on it for about 5 months. I've decided to power the heaters with V regs so that I can run the mosfets at a lower current. It was hot but sounded nice. I got several compliments on the sound at LSAF this year although it looked like Frankenstein's monster.
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